The present invention relates to aromatic diamine compounds which can be used as raw materials for polyimide, polyamide, bismaleimide or epoxy resins. The compounds can also be employed as curing agents. The invention also relates to a method for preparing the compounds.
Furthermore, the present invention relates to bismaleimide compounds which are useful as raw materials for heat-resistant resins, and which can be obtained from the aforementioned aromatic diamine compounds. The invention also relates to a method for preparing the compounds.
In addition, the present invention relates to thermosetting resin forming compositions, and ultimately the resins, which are obtained from the aforementioned aromatic diamine compounds and bismaleimide compounds, as well as a method for preparing the composition.
In recent years, raw materials for heat-resistant resins have been required to provide a combination of good thermal and mechanical properties, as well as certain other characteristics which composites should exhibit such as flexibility and moldability/workability.
In this regard, polyimide resins have been used. While providing some excellent properties, they typically exhibit poor moldability/workability.
An example of such a polyimide is an aromatic polyimide made by Du Pont and marketed under the tradename "Vespel". This polyimide can be prepared from 4,4'-diaminodiphenyl ether and pyromellitic anhydride. It is insoluble and unmeltable. Thus, when it is molded, a special procedure such as powder sinter molding must be used. Unfortunately, this molding technique cannot be easily used for the preparation of articles having complex shapes. During manufacturing of complex shaped articles, additional operations such as cutting are necessary. As a result the polyimide is difficult to mold and costs increase.
To address those drawbacks associated with polyimide resins, a variety of strategies have been formulated, primarily focusing on improving the diamine component of the raw materials. For example, there have been attempts to introduce an ether linkage group or an isopropylidene group into the molecule and to increase the molecular chain. Unfortunately, these techniques have not effectively provided the flexibility and moldability/workability characteristics necessary for composite materials.
A typical example of a bismaleimide is N,N'-(methylene-di-p-phenylene)bismaleimide disclosed in Japanese Patent Laid-open Nos. 47-8644 and 47-11500. However, this bismaleimide compound is substantially insoluble in common organic solvents such as ketone and petroleum solvents. And, when a polyimide resin is prepared using this compound, the occupation ratio of the polyimido group in the polymer structure is high. Therefore, the polymer is hard, brittle and provides extremely poor flexibility and high hygroscopicity. The effective application of the bismaleimide compounds is accordingly limited considerably.
Recently, in an effort to eliminate such disadvantages, much attention has been given to the development of long-chain bismaleimide compounds. For example, Japanese Patent Laid-open No. 63-500866 discloses a bismaleimide compound having three benzene rings and having the following structure represented by formula (X): ##STR3## In addition, Japanese Patent Laid-open No. 63-264566 discloses a bismaleimide compound having four benzene rings and having the following structure represented by the formula (XI): ##STR4##
However, even with these bismaleimide compounds and polymers prepared from the compounds, an effective balanced combination of heat resistance, flexibility, adhesion to a metal and inorganic materials, and workability is not provided.
Thermosetting resins having an imido structure have been effectively used to prepare molded articles having excellent electrical insulating properties, heat resistance and dimensional stability. Therefore, this type of resin has been utilized in many industrial fields.
However, thermosetting resins obtained by subjecting aromatic bismaleimides alone to heat polymerization are very brittle and provide poor flexibility, although they do provide excellent heat resistance. To address this drawback, attempts have been made to develop thermosetting resin forming compositions comprising an aromatic bismaleimide and an aromatic diamine. For example, a polyaminobismaleimide resin made by Rhone Poulenc, and marketed under the tradename "Kelimide" comprising N,N'-4,4'-diphenylmethane-bismaleimide and 4,4'-diaminodiphenylmethane has been widely utilized for impregnating varnishes, laminates and molded articles (See Japanese Patent Publication No. 46-23250). However, this type of thermosetting resin is still unsatisfactory in terms of impact resistance and flexibility. Furthermore, when these thermosetting resins are used as base materials for electrical and electronic parts, they exhibit poor moldability/workability and high hygroscopicity, which adversely affect electrical properties.